Abstract: The impoundment of Three Gorges Reservoir has changed the conditions of water release and sediment, and correspondingly changed the characteristics of water and sediment transport in the downstream channel. With 10day as the unit of data statistics, the changes of average runoff, sediment discharge and sediment concentration before and after the impounding were compared and analyzed. The analysis of the occurrence probability of high, medium and low water flow intervals showed that the flood flow interval frequency decreased more significantly as the distance from the dam grew larger. The sediment recovery of different flow levels are also analyzed. It is found that the sediment recovery degree of high and low flow levels are higher than that of middle flow level. Furthermore, through analysis on the changes of D50 of suspended sediment and size distribution of bed sediment, it is demonstrated that the bed surface coarsening is located mainly in Jingjiang river reach which is near the Three Gorges Project, and the D50 of suspended sediment was remarkably coarsened in the lower Jingjiang reach due to particle size exchange.

Key words: Three Gorges Reservoir , flow  , suspended sediment  , sediment concentration  , size distribution